Glass breakage detector

ABSTRACT

A device attachable to a plane of glass to set off an alarm in response to its breakage but immune to other vibrations. The device comprises a base attachable to the glass by an adhesive, a member carried by the base and spring-urged from a set to an alarm position, and a sensing element holding the member in its set position and responsive only to glass breakage to release the member. The sensing element comprises a curved spring fixed at one end and responsive only to the shock wave of the shattering glass to trigger the device, the spring being immune from triggering excitation normal to the glass plane.

United States Patent 1 1 McHenry 1 GLASS BREAKAGE DETECTOR [75]Inventor: Vincent J. Mcl-lenry, Farmington.

Mich.

[731 Assignee: Omni Spectra, Inc., Farmington,

Mich.

[22] Filed: May 17, 1973 21 Appl. No.: 361,207

[52] U.S. Cl 340/274 R; ZOO/61.84; ZOO/61.93;

200/6108 [51] Int. Cl. G08b 13/08 [58] Field of Search 340/276, 274 R,273;

ZOO/61.76, 6178, 61.79, 61.8, 61.84, 61.93, 223, 61.08; 116/75, 77, 67R, DlG. 18

[56] References Cited UNITED STATES PATENTS 3,706,090 12/1972 Callaghan340/273 1 Aug. 12, 1975 Primary ExaminerJohn W. Caldwell AssistantExaminer-william M. Wannisky Attorney, Agent, or FirmHarness, Dickey &Pierce 1 ABSTRACT A device attachable to a plane of glass to set off analarm in response to its breakage but immune to other vibrations. Thedevice comprises a base attachable to the glass by an adhesive, a membercarried by the base and spring-urged from a set to an alarm position,and a sensing element holding the member in its set position andresponsive only to glass breakage to release the member. The sensingelement comprises a curved spring fixed at one end and responsive onlyto the shock wave of the shattering glass to trigger the device, thespring being immune from triggering excitation nonnal to the glassplane.

20 Claims, 2 Drawing Figures CLASS BREAKAGE DETECTOR BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates to devices fordetecting glass breakage, particularly to mechanisms of the type whichwill set off an alarm when a pane of window glass is fractured orshattered.

2. Description of the Prior Art Various types of window sensors inintrusion detection systems include window foil, piezoelectrictransducers, variable current bridges and mechanical vibrators. Thewindow foil method uses thin metal foil mounted to the glass connectedto a normally closed alarm circuit. When the glass is broken, the foilgenerally breaks to provide the alarm. While reliable, this equipment iscostly to install and maintain, being subject for example to scars orcracks in the foil.

Piezoelectric devices work on the principle of an output voltagegenerated from a crystal by mechanical excitation. The devices generallyrequire adjustment when installed and always require a power supply andelectronic circuitry preceding the alarm circuit. The small outputvoltage of a piezoelectric device is usually insufficient to operatealarm contacts directly but must work through relay means.

Variable current bridge devices operate on the principle of currentbalance in a bridge circuit. Mechanical shock through a transducerchanges the balance in the bridge, thus changing the current level inthe alarm circuit. Such devices require a power supply, electroniccircuitry and an alarm circuit current regulator.

Mechanical vibrators have seldom been used but work on the principle ofa mechanical member being mounted to the glass surface and set intovibration by applied mechanical shock. Such devices in the past havebeen extremely difficult to adjust so that they will only respond tobreaking glass.

Among the patents collected in a novelty search on the subject matter ofthis invention, the following were noted but are not believed to affectthe patentability of the claims: Stelter U.S. Pat. No. 2,884,623; SwissPat. No. 277,847; Callaghan US. Pat. No. 3,706,090; Lupold et al. US.Pat. No. l,974,779; Traweek, Jr., US. Pat. No. 2,230,l70; White US. Pat.No. 3,441,925; and Colman US. Pat. No. 3,634,845.

BRIEF SUMMARY OF THE INVENTION It is an object of the present inventionto provide a novel and improved glass breakage detector which fulfillsthe need for a reliable, low cost sensor ideally suited for massproduction and responsive only to glass breakage.

It is another object to provide an improved glass breakage detector ofthis type which is immune from excitation normal to the plane of theglass so that an object striking the glass but not breaking it will notset off the alarm, and which cannot be magnetically defeated.

It is another object to provide an improved glass breakage detector ofthis type which utilizes the principle of a mechanically resonantsensing element.

It is a further object to provide an improved glass breakage detector ofthis character which requires no power supply other than that normallyprovided in the alarm circuit and also no electronic circuitry toperform its function.

It is also an object to provide an improved glass breakage detectorhaving these characteristics, which permits either a normally open ornormally closed cir cuit operation. or both, in the same device,requires no changes in alarm circuitry to allow its use, and providespositive contact closure and opening.

It is a further object to provide an improved glass breakage detector ofthis nature which will operate satisfactorily in either extremely low orextremely high ambient temperatures.

It is another object to provide an improved glass breakage detector ofthis nature which may be visually inspected and tested to determine itssetting and performance, and must be manually reset after it istriggered, thus permitting positive identification of the alarm locationwhen used as part of a group of detectors.

The invention centers around the use of a resonant sensing elementresponsive only to the shock wave which accompanies glass breakage butimmune to other vibrations. As illustrated, the invention comprises aswitch actuating member securable to the glass and spring-urged from aset position to an alarm or triggered position, contact means controlledby the member in response to said movement and a spiral resonant sensingelement holding the member in its set position and responsive only tothe shock wave attendant upon shattering of the glass to release themember. More specifically, the illustrated embodiment comprises a basesecurable to the glass surface, switch means mounted on the base, switchactuating means rotatably mounted on the base and spring-urged from itsset to its triggered position, and a curved spring fixed at one end andcarrying a detent normally holding the member in its set position, thespring being so constructed as to be immune from excitation normal tothe plane of the glass but responsive to the shock wave whichaccompanies glass shattering to release the member.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view incross section taken along the line 1-1 of FIG. 2 and showing the glassbreakage detector of this invention mounted on a pane of glass, partsbeing broken away;

FIG. 2 is a front elevational view of the device with the cover removed,with the switch actuating rotor in its set position;

FIG. 3 is a plan cross-sectional view taken along the line 33 of FIG. 2;and

FIG. 4 is a front elevational view similar to FIG. 2 with parts beingsectioned and showing the rotor in its triggered position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The glass breakage detector isgenerally indicated at l I and is intended to detect the fracturing orshattering of a pane of window glass partially. indicated at I2. Thedevice comprises a base 13 of circular shape having a substantially flatrear surface 14 securable to the inner surface IS of glass pane 12 bymeans of a bonding agent I6. The bonding agent is preferably of anonresilient nature which will not dry out or otherwise altercharacteristics with time in a manner which might affect the sensitivityof device II. The shear characteristics of bond 16 may be such that baseI3 is removable from glass I2 is desired. Although the location of thedevice on the glass is not critical, it is so mounted as to be easilyaccessible for wiring. The number of devices needed for a given panewill depend on its size. It has been found that a single detector II isadequate to protect a pane of glass up to 32 square feet in area. Asuitable location for the detector on a glass pane of typical size isabout 6 inches from one side and 6 inches from the top or bottom.

Base 13 has a central post 17 extending therefrom, the outer end ofwhich carries a cup-shaped cover 18 for the device. Cover 18 is securedto post 17 by a screw 19 and fits in a recess 21 around the edge of thebase. The outer surface of cover 18 is flat, and a circular window 22 inthe form of transparent cylindrical plastic member or the like isprovided on the front of the cover for purposes which will hereinafterappear.

A contact support 23 is secured to post 17 immediately inwardly of cover18. The support is of segmental shape, having four ribs 24 extendingoutwardly from a hub 25 secured to the post. Three contacts 26, 27 and28 are secured to support 23 between bridges 24 and extend toward base13. The contacts are of cylindrical shape and secured in position. Wireattaching terminal screws 29 are provided for the contacts.

The lower portion of base 13 has an extension 30 of arcuate shape, theouter end of which interfits with the edge of contact support 23. Thisextension is for the purpose of supporting electrical conductor wires(not shown) which lead in past cover 18 by means of radial grooves 31 inthe base and thence to axially extending grooves 32 which are formed inthe underside of extension 30. Although there are only three contacts,four wire access channels are provided for convenience purposes. Base I3is provided with a flattened portion 33 opposite extension 30 fororientation purposes during manufacture.

A switch actuating member in the form of a rotor 34 is rotatably mountedon post 17 inwardly of contact support 25. Both the rotor and contactsupport may be fabricated of an electrically insulative material. Thediameter of rotor 34 is almost as great as the inside diameter of cover18. The outer edge of the rotor is provided with an elongated recess 35in the vicinity of base extension 30 which limits its rotating movementbetween the set and triggered positions. The outer edge of rotor 34 isnotched as indicated at 36 to facilitate finger gripping. The rotorcarries a contact engaging wiper element 37 of arcuate shape havingcurved end portions 38 supported by posts 39. This spring-like elementwill connect contacts 26 and 27 when the rotor is in its set position asshown in FIG. 2, and contacts 27 and 28 when the rotor is triggered(FIG. 4). Thus the device may be used with either a normally open or anormally closed alarm circuit, or both. In the latter arrangement, onealarm circuit will supervise the other. A notch 40 is provided along theedge of rotor 34 for orientation purposes during manufacture.

A helical coil spring 41 is provided which surrounds hub 42 of rotor 34and has one end 43 fixed by insertion in an aperture of contact support23. The other end 44 of spring 41 extends into an aperture on rotor 34.Spring 4] urges rotor 34 in a counterclockwise direction from its setposition as shown in FIG. 2 to its triggered position of FIG. 4.

The means for holding rotor 34 in its set position comprises a pin 45carried by the rotor and a detent 46 carried by a glass breakage sensingelement generally indicated at 47. Pin 45 is eccentrically formed on acylindrical member 48 rotatably mounted in rotor 34. The rotationalposition of member 48 may be frictionally adjusted by turning themember, which is provided with a screwdriver slot 49. As seen in FIG. 3,member 48 is provided with a shoulder 5| engaging the forward surface ofrotor 34, and a cover 52 is mounted on pin 48. The purpose of this coveris to indicate the triggered position of the rotor through window 22,for which purpose it may be colored red as indicated in FIG. 2. Therotor 34 also carries a raised portion 53 which will be opposite window22 when the rotor is in its set position and is colored green. Together,cover 52 and raised portion 53 comprise visual indicia for the conditionof the device.

Preferably, the cross-sectional shape of pin 45 is semicircular as seenin FIG. 4 so as to present a sharp edge engaging detent 46. The detenthas a surface 54 which extends substantially radially when the device isset. This arrangement, plus the ability to adjust eccentric pin 45 byrotation of member 48, provides satisfactory sensitivity and adjustmentcontrol.

Sensing element 47 is a spring of generally spiral shape. The inner end55 of this spring extends radially inwardly and is wrapped around post17 between rotor 34 and base 13. A bushing 56 is mounted on the post andhas a slot 57 for receiving end 55 of the spring, the bushing holdingthe spring in fixed position. The crosssectional shape of spring 47 isseen in FIGS. 1 and 3 and is rectangular, with the long axis beingparallel to the rotational axis of rotor 34 and the short axisperpendicular thereto. Thus, the spring is substantially more flexiblein a plane parallel to the plane of glass 12 than it is normal to theglass plane. When a window glass is fractured or shattered, a high levelshock wave is transmitted in the plane of the glass. Element 47 is soconstructed as to be resonant to this shock wave, which will set theelement into strong vibration principally parallel to the plane of theglass.

Although the shape of spring 47 may be varied to suit individualrequirements, a suitable construction utilizes an Archimedes spiralextending from inner end 55 to detent 46 and an involute spiraloutwardly therefrom, the outer end 58 of the spring being curled arounditself and the total extent of the spring being approximately 270".

In use, device 11 will be set by removing cover 18 and rotating rotor 34clockwise. Half-round pin 45 will engage a beveled edge 59 on detent 46,flexing spring 47 out of the way until pin 45 snaps behind shoulder 54of detent 46. At the same time contact 37 will connect contacts 26 and27 and disconnect contacts 27 and 28, and green indicator 53 will bevisible through window 22 to show that the device is set. The setting ofrotor 34 will also tension spring 41 so that the rotor is urgedcounterclockwise.

Any vibration of the glass 12 normal to its plane which is notaccompanied by glass breakage will not affect the set position of thedevice. However, upon shattering or fracturing of the glass, theattendant shock wave and vibration in predominately low frequenciesgenerated in the plane of the glass will be transmitted through base 13and post 17 to sensing element 47. This will set it into strongvibration, principally parallel to the plane of the glass, retractingdetent 46 from pin 45 and permitting spring 41 to rotate rotor 34counterclockwise from its FIG. 2 to its FIG. 4 position. This willconnect contacts 27 and 28 and disconnect contacts 26 and 27, settingoff the alarm. It will also move red indicator 52 in front of window 22so that the triggered condition of the device is visible.

I claim:

1. In a glass breakage detector, a sensing element. means securing saidelement to the inside surface of the glass, the element extending fromsaid securing means, the shape of said element being such that movementof said securing means by the shock wave attendant only upon glassbreakage will set said element into strong resonant vibrationprincipally parallel to the plane of the glass, the shape of saidelement further being such that it is relatively immune to movement ofsaid securing means by vibrations normal to the glass plane, and meansconnected to said sensing element and movable from a normal set positionto a triggered position in which it initiates an alarm, saidlast-mentioned means being responsive to said vibrations of the sensingelement parallel to the glass plane to move to its triggered positionand thus initiate an alarm.

2. The combination according to claim 1, said sensing element being aspiral resonant element fixed only at its inner end.

3. The combination according to claim 1, said sensing element having across-sectional shape such that it is substantially more flexible in aplane parallel to the glass than normal to it.

4. The combination according to claim 1, said lastmentioned meanscomprising a member securable to the glass and spring-urged to move froma set position to a triggered position. and contact means controlled bythe member in response to said movement, said sensing element holdingthe member in its set position and responsive only to said vibrations torelease the member.

5. In a glass breakage detector, a base securable to the glass surface,switch means mounted on the base to initiate an alarm, switch actuatingmeans rotatably mounted on the base and spring-urged from its set to itstriggered position, and a curved spring fixed at one end and carrying adetent normally holding the member in its set position, the curvedspring being so constructed as to be immune from excitation normal tothe plane of the glass but responsive to the shock wave whichaccompanies glass shattering to release the member.

6. A glass breakage detector comprising a flat base secured to onesurface of the glass, at least two spaced switch contacts carried bysaid base. a switch actuating member carried by said base to initiate analarm, means constantly urging said member from a set position to atriggered position changing the conductive relation between saidcontacts, a detent normally holding said member in its set position, andan element secured to said base and connected to said detent, saidelement being so shaped as to be set into relatively strong resonantvibration principally in the plane of the glass in response to the shockwave transmitted to the base by the glass when it is fractured orshattered, whereby the detent will be moved to release the switchactuating member which is then permitted to move to its triggeredposition.

7. The combination according to claim 6, said sensing element comprisinga spring of generally spiral shape having its inner end fixed to saidbase and its outer end free, the cross-sectional shape of this saidspring being elongated in a direction normal to the glass plane.

8. The combination according to claim 7, said detent being carried by anintermediate portion of said spring.

9. The combination according to claim 8, the portion of said springbetween its inner fixed end and said detent having the shape of anArchimedes spiral, the portion outwardly of the detent having the shapeof an involute spiral.

10. The combination according to claim 8, the crosssectional shape ofsaid spring being rectangular, its outer end being curled around itself.

11. The combination according to claim 6, there being three contacts,said member being rotatably mounted on said base, said urging meanscomprising a helical spring.

12. in a glass breakage detector, a substantially flat base securable tothe surface of a plane of glass by a bonding agent, a central postcarried by said base, a cover removably securable to the outer end ofsaid post to enclose the elements of the device, a contact support fixedto said post and carrying a plurality of circumferentially arrangedcontacts, a switch actuating member to initiate an alarm comprising arotor rotatably mounted on said post, said rotor being movable between aset position in which it creates a certain conductive relation betweensaid contacts and a triggered position in which another conductiverelation is created, spring means constantly urging said rotor from itsset to its triggered position, a pin carried by said rotor, a detentengageable with said pin to hold the rotor in the set position, asensing element comprising a spiral spring fixed at its inner end tosaid post and carrying said detent at an intennediate portion, saidspring having a rectangular crosssectional shape with its long axisnormal to the plane of the glass, whereby the spring will exhibit a highdegree of immunity to vibrations normal to the plane of the glass butwill be set into resonant vibration by the shock wave created by glassbreakage sufficiently to cause said detent to release said pin.

13. The combination according to claim 12, there being threecircumferentially spaced contacts, said rotor carrying a wiper contactconnecting first and second fixed contacts when the rotor is in its setposition and second and third fixed contacts when it is in its triggeredposition.

14. The combination according to claim 12, said pin being eccentricallycarried by a rotatable member on said rotor, whereby the position of thepin may be adjusted with respect to the detent.

15. The combination according to claim 14, said pin being of half-roundcross-sectional shape with a sharp edge engageable with a shoulder onthe detent.

16. The combination according to claim 15, said detent having a beveledsurface engageable by the rounded portion of the pin when rotated towardits set position.

17. The combination according to claim 12, said cover being providedwith a window and visual indicia carried by the rotor and visiblethrough said window to indicate the set and triggered rotor positions.

18. The combination according to claim 12, said base having an axialextension inside said cover, and electrical conductor recesses formed insaid extension and leading to terminals on said contact support.

19. The combination according to claim 18, further provided withcoacting means on said rotor and base limiting movement of the rotor inboth directions.

20. The combination according to claim I9, said coacting meanscomprising an elongated recessed portion on the edge of said rotoradjacent said base extension.

1. In a glass breakage detector, a sensing element, means securing saidelement to the inside surface of the glass, the element extending fromsaid securing means, the shape of said element being such that movementof said securing means by the shock wave attendant only upon glassbreakage will set said element into strong resonant vibrationprincipally parallel to the plane of the glass, the shape of saidelement further being such that it is relatively immune to movement ofsaid securing means by vibrations normal to the glass plane, and meansconnected to said sensing element and movable from a normal set positionto a triggered position in which it initiates an alarm, saidlast-mentioned means being responsive to said vibrations of the sensingelement parallel to the glass plane to move to its triggered positionand thus initiate an alarm.
 2. The combination according to claim 1,said sensing element being a spiral resonant element fixed only at itsinner end.
 3. The combination according to claim 1, said sensing elementhaving a crosS-sectional shape such that it is substantially moreflexible in a plane parallel to the glass than normal to it.
 4. Thecombination according to claim 1, said last-mentioned means comprising amember securable to the glass and spring-urged to move from a setposition to a triggered position, and contact means controlled by themember in response to said movement, said sensing element holding themember in its set position and responsive only to said vibrations torelease the member.
 5. In a glass breakage detector, a base securable tothe glass surface, switch means mounted on the base to initiate analarm, switch actuating means rotatably mounted on the base andspring-urged from its set to its triggered position, and a curved springfixed at one end and carrying a detent normally holding the member inits set position, the curved spring being so constructed as to be immunefrom excitation normal to the plane of the glass but responsive to theshock wave which accompanies glass shattering to release the member. 6.A glass breakage detector comprising a flat base secured to one surfaceof the glass, at least two spaced switch contacts carried by said base,a switch actuating member carried by said base to initiate an alarm,means constantly urging said member from a set position to a triggeredposition changing the conductive relation between said contacts, adetent normally holding said member in its set position, and an elementsecured to said base and connected to said detent, said element being soshaped as to be set into relatively strong resonant vibrationprincipally in the plane of the glass in response to the shock wavetransmitted to the base by the glass when it is fractured or shattered,whereby the detent will be moved to release the switch actuating memberwhich is then permitted to move to its triggered position.
 7. Thecombination according to claim 6, said sensing element comprising aspring of generally spiral shape having its inner end fixed to said baseand its outer end free, the cross-sectional shape of this said springbeing elongated in a direction normal to the glass plane.
 8. Thecombination according to claim 7, said detent being carried by anintermediate portion of said spring.
 9. The combination according toclaim 8, the portion of said spring between its inner fixed end and saiddetent having the shape of an Archimedes spiral, the portion outwardlyof the detent having the shape of an involute spiral.
 10. Thecombination according to claim 8, the cross-sectional shape of saidspring being rectangular, its outer end being curled around itself. 11.The combination according to claim 6, there being three contacts, saidmember being rotatably mounted on said base, said urging meanscomprising a helical spring.
 12. In a glass breakage detector, asubstantially flat base securable to the surface of a plane of glass bya bonding agent, a central post carried by said base, a cover removablysecurable to the outer end of said post to enclose the elements of thedevice, a contact support fixed to said post and carrying a plurality ofcircumferentially arranged contacts, a switch actuating member toinitiate an alarm comprising a rotor rotatably mounted on said post,said rotor being movable between a set position in which it creates acertain conductive relation between said contacts and a triggeredposition in which another conductive relation is created, spring meansconstantly urging said rotor from its set to its triggered position, apin carried by said rotor, a detent engageable with said pin to hold therotor in the set position, a sensing element comprising a spiral springfixed at its inner end to said post and carrying said detent at anintermediate portion, said spring having a rectangular cross-sectionalshape with its long axis normal to the plane of the glass, whereby thespring will exhibit a high degree of immunity to vibrations normal tothe plane of the glass but will be set into resonant vibration bY theshock wave created by glass breakage sufficiently to cause said detentto release said pin.
 13. The combination according to claim 12, therebeing three circumferentially spaced contacts, said rotor carrying awiper contact connecting first and second fixed contacts when the rotoris in its set position and second and third fixed contacts when it is inits triggered position.
 14. The combination according to claim 12, saidpin being eccentrically carried by a rotatable member on said rotor,whereby the position of the pin may be adjusted with respect to thedetent.
 15. The combination according to claim 14, said pin being ofhalf-round cross-sectional shape with a sharp edge engageable with ashoulder on the detent.
 16. The combination according to claim 15, saiddetent having a beveled surface engageable by the rounded portion of thepin when rotated toward its set position.
 17. The combination accordingto claim 12, said cover being provided with a window and visual indiciacarried by the rotor and visible through said window to indicate the setand triggered rotor positions.
 18. The combination according to claim12, said base having an axial extension inside said cover, andelectrical conductor recesses formed in said extension and leading toterminals on said contact support.
 19. The combination according toclaim 18, further provided with coacting means on said rotor and baselimiting movement of the rotor in both directions.
 20. The combinationaccording to claim 19, said coacting means comprising an elongatedrecessed portion on the edge of said rotor adjacent said base extension.